Infant survivors of idiopathic respiratory distress syndrome (RDS) develop pulmonary residua which are believed to predispose these infants to more frequent and/or more severe respiratory infections. To assess this aspect of the long-term morbidity of RDS, we are systematically and prospectively evaluating the frequency, severity, and etiologies of acute respiratory illnesses in survivors of RDS and pre-term infants who did not have RDS compared to normal, full-term, infants matched for sex and season of birth.